German Patent No. 19928037 describes an electrically heatable glow plug for internal-combustion engines that includes a glow tube that is closed at its end and is corrosion-resistant, and that accommodates a filling of a compressed, electrically nonconductive powder in which there is embedded an electrically conductive filament. The filament includes a heating coil. This heating coil is formed from an iron-chromium-aluminum alloy. In the area of the heating coil, the electrically conductive filament is hardened on its surface. In this way, the filament can withstand the mechanical stress during the compression process without damage.
German Patent No. 19756988 describes an electrically heatable glow plug for internal-combustion engines that has a glow element made of a corrosion-resistant metal jacket. In the glow element there is contained a compressed powder filling. An electrically conductive filament is embedded in the filling. In order to increase the life span of the filament, a getter material is provided in the glow element for the binding of the oxygen contained in the compressed powder filling. The getter material can be distributed in the compressed powder filling in the form of electrically non-conductive particles. These particles can be made of silicon or metal oxides of metals that oxidize in several oxidation stages and that have a higher affinity to oxygen than does the filament material; in the initial state, the getter material can contain the metal oxides in their first oxidation stage.
European Published Patent Application No. 0079385 describes a heating element in which a filament is situated in a sheath and is embedded in an electrically insulating powder. The powder has 0.1 to 10 weight percent of an oxide, and in this way prevents the oxidation of the metallic portion of the filament.